This invention relates to circle cutting apparatus, and more particularly, to an apparatus for supporting a cutting torch for accurately cutting circular bolt holes in metal plate or the like.
In the construction of metal boilers and other pressure vessels for the use in the petro-chemical and refining industry and in other industries requiring large pressure vessels it is necessary to cut small circular holes in the heavy metal plate that forms the base rings of such vessels. The base ring flanges of such boilers or pressure vessels may be four inches to one foot in width, most commonly being on the order of 4-6 inches wide. Often the material is metal plate that may vary anywhere from 3/8 to 4 inches thick. The holes in the base ring flanges are for mounting bolts to mount the pressure vessel or boiler to a suitable structure or base. Such mounting bolt holes are typically 11/2 to 21/2 inches in diameter, although they may occasionally be smaller, and sometimes it is necessary that they be of a larger diameter. On occasion the holes must be beveled to meet construction requirements. These flange rings may be anywhere from a few feet to 10 or 12 feet in diameter and because of the large size and weight of the flanges, it is difficult to drill bolt holes of the size required through the flanges since twist drill machines to accomodate such diameter holes are not commonly portable, and it is difficult or sometimes impossible to take a large flange ring to a stationary drill press that can drill the desired size holes.
Accordingly, in the past it has been common to cut such bolt holes manually by using an acetylene torch. There are disadvantages to manually cutting such bolt holes by hand with a torch, however, since it takes a great deal of developed skill for a torch operator to be able to cut a smooth and perpendicular bolt hole, and the smaller the diameter of the hole the more difficult it is to cut a smooth bolt hole. Any slight angle between the torch and plate will result in an undesirable beveled hole. Further, the speed at which the circular bolt hole is to be cut varies depending on the composition of the metal plate and its thickness, and it is difficult for an operator to be consistent in his cutting speed and circular motion from bolt hole to bolt hole. In addition, often the bolt hole cuts are so rough that they must be further machined and polished and touched up with the torch, or in some cases the tolerances are out of specification, and the flange cannot be utilized. All of this leads to a great waste of time by the torch operator, and a loss in labor and materials due to the non-uniformity of the bolt holes cut in the flanges and the wasting of material for non-acceptable jobs.
The prior art includes many torch cutting machines for cutting intricate shapes and designs in metal plate, these torch machines often being controlled by a computer or a numerically controlled machine that can cut large intricate patterns. Such prior art is exemplified by the following U.S. Pat. Nos.: 4,121,808 (Cardea); 3,665,148 (Yasenchak et al.); 3,614,078 (Hepkr); 2,816,848 (Maxon); and 2,496,110 (Thurman). In addition, U.S. Pat. No. 4,053,145 (Steele) discloses a cutting torch guide for providing means for effecting circular cutouts in large vessels or large diameter pipe without the need of a lay-out other than fixing a working point and providing multiple adjustments so the cuts may be made of the desired diameter as well as having the desired bevel. The cutting torch guide utilizes a center shaft for marking the center of the area to be cut on the curved surface of such large vessels or large diameter pipe. However, the disclosed apparatus, while certainly utilizable to cut circular cutouts in the side of a large diameter vessel or pipe is not suitable for cutting rather small diameter holes in flange rings or other members.
U.S. Pat. No. 4,021,025 (Frame) discloses a circle cutting apparatus particularly adaptable for the cutting of circles and arcs in metal plate with a cutting torch. The device comprises a circular platform which is attached to the plate to be cut and a torch or cutting implement which is radially adjustable with respect to the platform, the cutting apparatus also being movable in a circular path with respect to the platform. The disclosed device is suitable for cutting rather large diameter circles, and while it may be possible to cut rather small diameter circles with the device, its size and construction, demanding a large circular platform and mounting area, would render it useless for use in cutting small circular bolt holes on rather narrow flange rims.
Accordingly, one primary feature of the present invention is to provide a portable hole cutting apparatus for cutting circular holes in metal plate such as narrow flange rims.
Another feature of the present invention is to provide a circle center marking means to locate the exact center of the circular bolt hole to be cut to aid in positioning the portable apparatus.
Yet another feature of the present invention is to provide a torch holding bracket that is transversely adjustable for varying the radius of the selected bolt hole to be cut by the torch.
Still another feature of the present invention is to provide drive means that can vary the speed of rotation of the torch during the cutting process.
Yet another feature of the present invention is to provide a bolt hole cutting apparatus that will consistently cut straight, smooth holes in metal plate.
Still another feature of the present invention is to provide a bolt hole cutting apparatus that can cut beveled holes in metal plate at a consistent desired angle of bevel.